1. Field of the Invention
The present invention relates to a roll film carrier applicable to a reader or a reader printer. More particularly, it relates to a roll film carrier capable of stopping a roll film by detecting its trailing end or a mid-way retrieval position.
2. Description of the Prior Art
As disclosed in U.S. Pat. No. 4,166,239, it is taken as one of the most important control functions to detect the trailing end of a roll film or a mid-way desired retrieval position to stop film feeding thereby when operation such as winding and rewinding of the roll film is to be controlled in a reader or reader printer using roll film.
This is because where the film feeding is done by a driving device such as a motor, regardless of whether each frame of the roll film is retrieved automatically or visually, it is possible that the roll film is wound up to the trailing end due to inadvertence of or mis-manipulation by the user. Especially when the other end of the roll film is fixed to the reel shaft, such excessive winding possibly causes troubles such as breakage of roll film, damage to its drive system and overheating of the motor.
In order to prevent the aforesaid defects, there is proposed in the U.S. Pat. No. 4,068,934 a method in which a special mark such as end mark is put in the vicinity of the trailing end of roll film so that, when the mark is detected by a mark detecting means, a stop signal is transmitted to the roll film driving device. According to Jap. Pat. Appl. Publication No. Sho-46-43186, on the other hand, a detection means is used to detect the mark for counting put in each frame of roll film. Proposed therein is a method by the use of a mark detection means to determine the time interval between two adjacent marks detected and a timer means with a predetermined time interval set thereon wherein when said next mark is not detected within said predetermined time interval, it is judged that there is no more frame and the roll film driving device is thereupon stopped. In the abovementioned system it is also possible to stop driving of the roll film also at any mid-way retrieval position by proper selection of the time interval set on the timer means.
In any of these control systems, however, it is necessary to put some mark to the roll film and also provide a mark detecting means and this means an increased cost of the roll film as well as the roll film carrier. This, at the same time, means another drawback of requiring a control device, whose control circuit may possibly be highly complicated.
The method disclosed in U.S. Pat. No. 4,068,934 has a drawback of being inconvenient practically in that, when frames are to be cut off from or added to a roll film, the mark for detecting the trailing end has to be shifted each time accordingly.
In the system disclosed in Jap. Pat. Appl. Publication No. Sho-46-43186, on the other hand, it is required to vary the time interval set on the timer means according to variation of the roll film's feeding speed or alternatively set said time interval to match the lowest film feeding speed with an increased wasteful length of film from the trailing end thereof.